.MOBI domain denotes Mobility. Using such domain name for your website makes it easy for site visitor to know your website is either meant for mobile devices or your business is a mobile business.
For mobile version of website
80% of does who make use of the internet do so from their mobile phones. So it is quite important that you make sure your website fits various mobile device screen sizes and resolution for a better user experience. Buying a .MOBI domain name for the mobile version of your website make it much easy for users to navigate your website when they are on mobile device.
For a food truck or any business on wheels
The MOBI also means for something to be in motion. Using a .MOBI domain name also tells viewers that your business is a mobile business that is not fixed at a particular location. Example of such businesses includes; food trucks, newspaper delivery service, freight company, etc.
For wap mobile websites
Before the advancement in mobile phone technology. Most website people visit for their music, movie or game download are known as mobile websites. These sites won't open on a computer. If you are owner of such website or you intent on building ones. Using a .MOBI domain name for such website seems very appropriate.